How a packaging figure is manufactured
Magnification is the focal length of the telescope divided by the focal length of the eyepiece. Supply a very short eyepiece and the quotient is large. Supply a very short eyepiece of simple design, and add a Barlow to the calculation, and it is larger still.
Every step of that is arithmetically correct. What the figure conceals is that the eyepiece producing it has almost no eye relief, a narrow field and a tiny exit pupil, and that the aperture in front of it cannot resolve enough detail to fill the enlargement.
Two ceilings sit below almost every advertised figure. The optical one, conventionally put at about twice the aperture in millimetres. And the atmospheric one, which on most nights is lower still.
What it does not promise
Detail. Past the aperture’s limit, more magnification enlarges a blur — the image gets bigger, dimmer and no sharper, and small features that were visible at lower power disappear.
Usability. At very small exit pupils the eye struggles, floaters become visible, and holding the head in position becomes the hardest part of the observation.
And it promises nothing about the telescope, which is the whole difficulty: two instruments of very different quality can print the same number.
What this site publishes instead
The aperture and the focal length, both as the maker gives them. The division belongs to the reader and to whichever eyepiece they actually own, and no page here reproduces a packaging magnification as though it were a specification.
The figure appears on this shelf most often where the buyer is least able to judge it — telescopes sold for children, travel scopes, and the cheaper end of every family — which is why it has a page of its own rather than a footnote.
The questions that keep arriving
So the number is a lie?
Not exactly, and that is what makes it effective. The division is correct. What is missing is that the eyepiece chosen to produce it delivers an image too dim and too soft to use, and that the aperture cannot support the figure in any case.
What should be printed instead?
The aperture and the focal length. From those a reader can calculate what any eyepiece will give, which is the calculation the box has made on their behalf with an eyepiece they would not have chosen.
Do binoculars have the same problem?
Far less, because the magnification of a pair of binoculars is fixed by its design and appears in its name honestly. The equivalent overclaim there is a very small aperture behind a high magnification.
Last reviewed 17 September 2026